Dual flush cistern mechanism

Abstract

The present invention discloses a dual flush cistern mechanism in which a hollow central stem functions as a flush valve operating member, a slide for a float and an overflow pipe. The float is retained on the stem by a releasable latch during normal operation. During reduced volume flush operation the latch is released, the float drops with the level of water in the cistern sliding along the raised stem until it strikes a projection thereby lowering the stem and prematurely closing the flush valve.

What I claim is: 
     
       1. A dual flush cistern mechanism comprising a substantially vertical stem mounted for substantially vertical movement above a flush valve of said cistern and having a flush valve seal located at its lower end; a float slidably mounted on said stem intermediate the ends thereof; a first lever arm pivotably connected to said stem at a location spaced from a first pivot in said cistern for said first lever arm, and being pivotable by each of a first and a second operating mechanism to raise said stem to open said flush valve; a second lever arm pivotable by said second operating mechanism about a second pivot in said cistern and carrying a latch member releasably engageable with said float in a high operating position, and a projection extending from said stem to limit the travel of said float into a low operating position; wherein said first operating mechanism is operable to raise said stem with said float retained in said high operating position by said latch member to open said flush valve for a first duration; and wherein said second operating mechanism is operable to substantially simultaneously raise said stem to open said flush valve to drain water from said cistern and release said latch member whereby said float drops with the water level in said cistern until said float engages said stem projection to move said stem downwardly and close said flush valve before the expiration of said first duration, said float being buoyantly movable from said low to said high position to re-engage said latch member with said float when said cistern is re-filled with water, and said first and second pivots each having a longitudinal axis which is stationary with respect to said cistern. 
     
     
       2. A mechanism as claimed in claim 1 wherein said first lever arm comprises a pair of levers having an upwardly opening V-shaped channel member extending across said pair of levers at one end, the other end of said levers being pivotally connected to said stem and said first pivot being located between the ends of said pair of levers. 
     
     
       3. A mechanism as claimed in claim 2 wherein said cistern has a top and said first operating mechanism comprises a first spring loaded button mounted in said top and a first connecting rod extending between said first button and said channel member, whereby depressing said first button pivots said pair of levers to raise said stem. 
     
     
       4. A mechanism as claimed in claim 3 wherein said second operating mechanism comprises a second spring loaded button mounted in said top and a second connecting rod extending between said second button and said channel member, said second connecting rod having a lug engageable with said second lever arm following depressing of said second button to pivot said second lever arm about said second, pivot and release said latch member. 
     
     
       5. A mechanism as claimed in claim 4 wherein said lug engages said second lever arm via a link pivoted adjacent it mid point, said lug depressing one half of said link to move said second lever arm, and said link returning to its original level position under the weight of the other half of said link. 
     
     
       6. A mechanism as claimed in claim 1 wherein said stem is hollow and said flush valve has a seal which is substantially annular whereby said stem comprises an overflow pipe for said cistern. 
     
     
       7. The mechanism as claimed in claim 6 wherein said stem has a rectangular cross-section. 
     
     
       8. A mechanism as claimed in claim 1 wherein said float is an open ended tube having an interior sleeve through which said stem passes and a web which connects said sleeve and tube to provide two volumes, an upper one which retains water and a lower one which retains air to respectively provide oppositively directed gravitational and buoyant forces. 
     
     
       9. A mechanism as claimed in claim 1, wherein said first and second pivots engage the interior of the cistern.